This project combines a basic research component aimed at understanding how muscle genes are regulated, with an applied component aimed at designing regulatory cassettes for expressing therapeutic proteins in striated muscle. Prior basic studies concentrated primarily on understanding how the mouse M-creatine kinase (MCK) gene enhancer and promoter control MCK expression in skeletal and cardiac muscle. These studies will continue but much of our future effort will be directed toward mapping three additional regulatory regions which confer higher transcriptional activity to the enhancer-promoter complex, and a fourth region which confers gene copy number-dependent expression. Control elements within these regions will be identified and these sequences will then be used to identify and understand the function of their associated transcription factors. Applied aspects of the project utilize the basic information above, together with published data concerning other striated muscle genes, to construct regulatory cassettes that will be useful in treating skeletal and cardiac muscle diseases, and in therapeutic situations which could benefit from using skeletal muscle as a source of secreted proteins; e.g., hormone and clotting factor deficiency diseases, and tissue healing. Goals for these studies are to optimize the transcriptional activity of cassettes designed to function in different striated muscle types, while simultaneously maintaining tight muscle-specific transcription so as to prevent therapeutic gene expression in immune system and other non-muscle cells that may be inadvertently transduced and damaged by mis-targeted gene therapy vectors. Two additional goals are to build miniature regulatory cassettes that will be compatible with packaging therapeutic cDNAs such as mini- and micro-dystrophins into AAV and other small viral vectors, and to build high activity muscle-specific cassettes expressing externally regulatable transcription factors that will selectively transcribe therapeutic cDNAs in response to non-harmful drugs, thus permitting the external manipulation of therapeutic gene product levels.